Efficient PLMN selection upon authentication failure for each network slice in roaming network

ABSTRACT

Provided are a method and device for efficient public land mobile network (PLMN) selection upon authentication failure for each network slice in a roaming network. A user equipment (UE) receives a registration rejection message from an access and mobility management function (AMF) of a first PLMN. The registration rejection message includes rejected network slice selection assistance information (NSSAI) including first single NSSAI (S-NSSAI) and cause value #62 for the rejected NSSAI. The UE: generates second requested NSSAI including second S-NSSAI on the basis that i) the UE does not have allowed NSSAI and configured NSSAI, and ii) default configured NSSAI includes the second S-NSSAI that is not included in the rejected NSSAI and corresponds to a network slice of which the UE requests registration; and transmits a second registration request message including the second requested NSSAI to the AMF of the first PLMN.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of International Application No. PCT/KR2021/005697 filed on May 7, 2021, which claims priority to Korean Patent Application No. 10-2020-0062496 filed on May 25, 2020, the contents of which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present disclosure relates to efficient public land mobile network (PLMN) selection upon authentication failure for each network slice in a roaming network.

BACKGROUND

3rd generation partnership project (3GPP) long-term evolution (LTE) is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3GPP LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.

Work has started in international telecommunication union (ITU) and 3GPP to develop requirements and specifications for new radio (NR) systems. 3GPP has to identify and develop the technology components needed for successfully standardizing the new RAT timely satisfying both the urgent market needs, and the more long-term requirements set forth by the ITU radio communication sector (ITU-R) international mobile telecommunications (IMT)-2020 process. Further, the NR should be able to use any spectrum band ranging at least up to 100 GHz that may be made available for wireless communications even in a more distant future.

The NR targets a single technical framework addressing all usage scenarios, requirements and deployment scenarios including enhanced mobile broadband (eMBB), massive machine-type-communications (mMTC), ultra-reliable and low latency communications (URLLC), etc. The NR shall be inherently forward compatible.

A network slice refers to a logical network that provides specific network capabilities and network characteristics. More specifically, a network slice is a network structure that enables multiplexing of virtualized independent logical networks in the same physical network infrastructure. Each network slice is a separate end-to-end network tailored to meet the various requirements requested by a specific application. The network slice enables various services to be provided to various terminals with different properties.

SUMMARY

When network slice specific authentication and authorization fails in a roaming environment, an issue in which unnecessary PLMN selection is repeated may occur. A method for efficiently performing PLMN selection may be required.

In an aspect, a method performed by a user equipment (UE) operating in a wireless communication system is provided. The method includes obtaining default configured network slice selection assistance information (NSSAI) which can be used in a first public land mobile network (PLMN), generating first requested NSSAI including a first single NSSAI (S-NSSAI) corresponding to a network slice to which the UE requests to register with, transmitting, to an access and mobility management function (AMF) of the first PLMN, a first registration request message including the first requested NSSAI, receiving, from the AMF of the first PLMN, a registration reject message in response to the first registration request message. The registration reject message includes rejected NSSAI including the first S-NSSAI, the registration reject message includes a cause value #62 for the rejected NSSAI, and the cause value #62 indicates “No network slices available”. The method includes, based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with, generating second NSSAI including the second S-NSSAI, and transmitting, to the AMF of the first PLMN, a second registration request message including the second requested NSSAI.

In another aspect, an apparatus for implementing the above method is provided.

The present disclosure can have various advantageous effects.

For example, by determining the S-NSSAI which can be transmitted based on the default configured NSSAI, unnecessary PLMN selection procedures and registration procedures can be efficiently removed.

For example, when the UE fails in the current access network due to network slice specific authentication failure in the roaming state and selects a PLMN again, it does not select an unnecessary PLMN to fail again, so that the PLMN selection can be performed more efficiently.

Advantageous effects which can be obtained through specific embodiments of the present disclosure are not limited to the advantageous effects listed above. For example, there may be a variety of technical effects that a person having ordinary skill in the related art can understand and/or derive from the present disclosure.

Accordingly, the specific effects of the present disclosure are not limited to those explicitly described herein, but may include various effects that may be understood or derived from the technical features of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example of a communication system to which implementations of the present disclosure is applied.

FIG. 2 shows an example of wireless devices to which implementations of the present disclosure is applied.

FIG. 3 shows an example of a wireless device to which implementations of the present disclosure is applied.

FIG. 4 shows an example of UE to which implementations of the present disclosure is applied.

FIG. 5 shows an example of 5G system architecture to which implementations of the present disclosure is applied.

FIGS. 6 and 7 show an example of a registration procedure to which implementations of the present disclosure is applied.

FIG. 8 shows an example of a situation to which the implementation of the present disclosure is applied.

FIG. 9 shows an example of a method performed by a UE to which the first implementation of the present disclosure is applied.

FIGS. 10 and 11 show an example of an SOR transparent container IE according to the third implementation of the present disclosure.

DETAILED DESCRIPTION

The following techniques, apparatuses, and systems may be applied to a variety of wireless multiple access systems. Examples of the multiple access systems include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, a single carrier frequency division multiple access (SC-FDMA) system, and a multicarrier frequency division multiple access (MC-FDMA) system. CDMA may be embodied through radio technology such as universal terrestrial radio access (UTRA) or CDMA2000. TDMA may be embodied through radio technology such as global system for mobile communications (GSM), general packet radio service (GPRS), or enhanced data rates for GSM evolution (EDGE). OFDMA may be embodied through radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, or evolved UTRA (E-UTRA). UTRA is a part of a universal mobile telecommunications system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA in DL and SC-FDMA in UL. Evolution of 3GPP LTE includes LTE-A (advanced), LTE-A Pro, and/or 5G new radio (NR).

For convenience of description, implementations of the present disclosure are mainly described in regards to a 3GPP based wireless communication system. However, the technical features of the present disclosure are not limited thereto. For example, although the following detailed description is given based on a mobile communication system corresponding to a 3GPP based wireless communication system, aspects of the present disclosure that are not limited to 3GPP based wireless communication system are applicable to other mobile communication systems.

For terms and technologies which are not specifically described among the terms of and technologies employed in the present disclosure, the wireless communication standard documents published before the present disclosure may be referenced.

In the present disclosure, “A or B” may mean “only A”, “only B”, or “both A and B”. In other words, “A or B” in the present disclosure may be interpreted as “A and/or B”. For example, “A, B or C” in the present disclosure may mean “only A”, “only B”, “only C”, or “any combination of A, B and C”.

In the present disclosure, slash (/) or comma (,) may mean “and/or”. For example, “A/B” may mean “A and/or B”. Accordingly, “A/B” may mean “only A”, “only B”, or “both A and B”. For example, “A, B, C” may mean “A, B or C”.

In the present disclosure, “at least one of A and B” may mean “only A”, “only B” or “both A and B”. In addition, the expression “at least one of A or B” or “at least one of A and/or B” in the present disclosure may be interpreted as same as “at least one of A and B”.

In addition, in the present disclosure, “at least one of A, B and C” may mean “only A”, “only B”, “only C”, or “any combination of A, B and C”. In addition, “at least one of A, B or C” or “at least one of A, B and/or C” may mean “at least one of A, B and C”.

Also, parentheses used in the present disclosure may mean “for example”. In detail, when it is shown as “control information (PDCCH)”, “PDCCH” may be proposed as an example of “control information”. In other words, “control information” in the present disclosure is not limited to “PDCCH”, and “PDDCH” may be proposed as an example of “control information”. In addition, even when shown as “control information (i.e., PDCCH)”, “PDCCH” may be proposed as an example of “control information”.

Technical features that are separately described in one drawing in the present disclosure may be implemented separately or simultaneously.

Although not limited thereto, various descriptions, functions, procedures, suggestions, methods and/or operational flowcharts of the present disclosure disclosed herein can be applied to various fields requiring wireless communication and/or connection (e.g., 5G) between devices.

Hereinafter, the present disclosure will be described in more detail with reference to drawings. The same reference numerals in the following drawings and/or descriptions may refer to the same and/or corresponding hardware blocks, software blocks, and/or functional blocks unless otherwise indicated.

FIG. 1 shows an example of a communication system to which implementations of the present disclosure is applied.

The 5G usage scenarios shown in FIG. 1 are only exemplary, and the technical features of the present disclosure can be applied to other 5G usage scenarios which are not shown in FIG. 1.

Three main requirement categories for 5G include (1) a category of enhanced mobile broadband (eMBB), (2) a category of massive machine type communication (mMTC), and (3) a category of ultra-reliable and low latency communications (URLLC).

Referring to FIG. 1, the communication system 1 includes wireless devices 100 a to 100 f, base stations (BSs) 200, and a network 300. Although FIG. 1 illustrates a 5G network as an example of the network of the communication system 1, the implementations of the present disclosure are not limited to the 5G system, and can be applied to the future communication system beyond the 5G system.

The BSs 200 and the network 300 may be implemented as wireless devices and a specific wireless device may operate as a BS/network node with respect to other wireless devices.

The wireless devices 100 a to 100 f represent devices performing communication using radio access technology (RAT) (e.g., 5G new RAT (NR)) or LTE) and may be referred to as communication/radio/5G devices. The wireless devices 100 a to 100 f may include, without being limited to, a robot 100 a, vehicles 100 b-1 and 100 b-2, an extended reality (XR) device 100 c, a hand-held device 100 d, a home appliance 100 e, an IoT device 100 f, and an artificial intelligence (AI) device/server 400. For example, the vehicles may include a vehicle having a wireless communication function, an autonomous driving vehicle, and a vehicle capable of performing communication between vehicles. The vehicles may include an unmanned aerial vehicle (UAV) (e.g., a drone). The XR device may include an AR/VR/Mixed Reality (MR) device and may be implemented in the form of a head-mounted device (HMD), a head-up display (HUD) mounted in a vehicle, a television, a smartphone, a computer, a wearable device, a home appliance device, a digital signage, a vehicle, a robot, etc. The hand-held device may include a smartphone, a smartpad, a wearable device (e.g., a smartwatch or a smartglasses), and a computer (e.g., a notebook). The home appliance may include a TV, a refrigerator, and a washing machine. The IoT device may include a sensor and a smartmeter.

In the present disclosure, the wireless devices 100 a to 100 f may be called user equipments (UEs). A UE may include, for example, a cellular phone, a smartphone, a laptop computer, a digital broadcast terminal, a personal digital assistant (PDA), a portable multimedia player (PMP), a navigation system, a slate personal computer (PC), a tablet PC, an ultrabook, a vehicle, a vehicle having an autonomous traveling function, a connected car, an UAV, an AI module, a robot, an AR device, a VR device, an MR device, a hologram device, a public safety device, an MTC device, an IoT device, a medical device, a FinTech device (or a financial device), a security device, a weather/environment device, a device related to a 5G service, or a device related to a fourth industrial revolution field.

The UAV may be, for example, an aircraft aviated by a wireless control signal without a human being onboard.

The VR device may include, for example, a device for implementing an object or a background of the virtual world. The AR device may include, for example, a device implemented by connecting an object or a background of the virtual world to an object or a background of the real world. The MR device may include, for example, a device implemented by merging an object or a background of the virtual world into an object or a background of the real world. The hologram device may include, for example, a device for implementing a stereoscopic image of 360 degrees by recording and reproducing stereoscopic information, using an interference phenomenon of light generated when two laser lights called holography meet.

The public safety device may include, for example, an image relay device or an image device that is wearable on the body of a user.

The MTC device and the IoT device may be, for example, devices that do not require direct human intervention or manipulation. For example, the MTC device and the IoT device may include smartmeters, vending machines, thermometers, smartbulbs, door locks, or various sensors.

The medical device may be, for example, a device used for the purpose of diagnosing, treating, relieving, curing, or preventing disease. For example, the medical device may be a device used for the purpose of diagnosing, treating, relieving, or correcting injury or impairment. For example, the medical device may be a device used for the purpose of inspecting, replacing, or modifying a structure or a function. For example, the medical device may be a device used for the purpose of adjusting pregnancy. For example, the medical device may include a device for treatment, a device for operation, a device for (in vitro) diagnosis, a hearing aid, or a device for procedure.

The security device may be, for example, a device installed to prevent a danger that may arise and to maintain safety. For example, the security device may be a camera, a closed-circuit TV (CCTV), a recorder, or a black box.

The FinTech device may be, for example, a device capable of providing a financial service such as mobile payment. For example, the FinTech device may include a payment device or a point of sales (POS) system.

The weather/environment device may include, for example, a device for monitoring or predicting a weather/environment.

The wireless devices 100 a to 100 f may be connected to the network 300 via the BSs 200. An AI technology may be applied to the wireless devices 100 a to 100 f and the wireless devices 100 a to 100 f may be connected to the AI server 400 via the network 300. The network 300 may be configured using a 3G network, a 4G (e.g., LTE) network, a 5G (e.g., NR) network, and a beyond-5G network. Although the wireless devices 100 a to 100 f may communicate with each other through the BSs 200/network 300, the wireless devices 100 a to 100 f may perform direct communication (e.g., sidelink communication) with each other without passing through the BSs 200/network 300. For example, the vehicles 100 b-1 and 100 b-2 may perform direct communication (e.g., vehicle-to-vehicle (V2V)/vehicle-to-everything (V2X) communication). The IoT device (e.g., a sensor) may perform direct communication with other IoT devices (e.g., sensors) or other wireless devices 100 a to 100 f.

Wireless communication/connections 150 a, 150 b and 150 c may be established between the wireless devices 100 a to 100 f and/or between wireless device 100 a to 100 f and BS 200 and/or between BSs 200. Herein, the wireless communication/connections may be established through various RATs (e.g., 5G NR) such as uplink/downlink communication 150 a, sidelink communication (or device-to-device (D2D) communication) 150 b, inter-base station communication 150 c (e.g., relay, integrated access and backhaul (IAB)), etc. The wireless devices 100 a to 100 f and the BSs 200/the wireless devices 100 a to 100 f may transmit/receive radio signals to/from each other through the wireless communication/connections 150 a, 150 b and 150 c. For example, the wireless communication/connections 150 a, 150 b and 150 c may transmit/receive signals through various physical channels. To this end, at least a part of various configuration information configuring processes, various signal processing processes (e.g., channel encoding/decoding, modulation/demodulation, and resource mapping/de-mapping), and resource allocating processes, for transmitting/receiving radio signals, may be performed based on the various proposals of the present disclosure.

AI refers to the field of studying artificial intelligence or the methodology that can create it, and machine learning refers to the field of defining various problems addressed in the field of AI and the field of methodology to solve them. Machine learning is also defined as an algorithm that increases the performance of a task through steady experience on a task.

Robot means a machine that automatically processes or operates a given task by its own ability. In particular, robots with the ability to recognize the environment and make self-determination to perform actions can be called intelligent robots. Robots can be classified as industrial, medical, home, military, etc., depending on the purpose or area of use. The robot can perform a variety of physical operations, such as moving the robot joints with actuators or motors. The movable robot also includes wheels, brakes, propellers, etc., on the drive, allowing it to drive on the ground or fly in the air.

Autonomous driving means a technology that drives on its own, and autonomous vehicles mean vehicles that drive without user's control or with minimal user's control. For example, autonomous driving may include maintaining lanes in motion, automatically adjusting speed such as adaptive cruise control, automatic driving along a set route, and automatically setting a route when a destination is set. The vehicle covers vehicles equipped with internal combustion engines, hybrid vehicles equipped with internal combustion engines and electric motors, and electric vehicles equipped with electric motors, and may include trains, motorcycles, etc., as well as cars. Autonomous vehicles can be seen as robots with autonomous driving functions.

Extended reality is collectively referred to as VR, AR, and MR. VR technology provides objects and backgrounds of real world only through computer graphic (CG) images. AR technology provides a virtual CG image on top of a real object image. MR technology is a CG technology that combines and combines virtual objects into the real world. MR technology is similar to AR technology in that they show real and virtual objects together. However, there is a difference in that in AR technology, virtual objects are used as complementary forms to real objects, while in MR technology, virtual objects and real objects are used as equal personalities.

NR supports multiples numerologies (and/or multiple subcarrier spacings (SCS)) to support various 5G services. For example, if SCS is 15 kHz, wide area can be supported in traditional cellular bands, and if SCS is 30 kHz/60 kHz, dense-urban, lower latency, and wider carrier bandwidth can be supported. If SCS is 60 kHz or higher, bandwidths greater than 24.25 GHz can be supported to overcome phase noise.

The NR frequency band may be defined as two types of frequency range, i.e., FR1 and FR2. The numerical value of the frequency range may be changed. For example, the frequency ranges of the two types (FR1 and FR2) may be as shown in Table 1 below. For ease of explanation, in the frequency ranges used in the NR system, FR1 may mean “sub 6 GHz range”, FR2 may mean “above 6 GHz range,” and may be referred to as millimeter wave (mmW).

TABLE 1 Frequency Range Corresponding frequency designation range Subcarrier Spacing FR1  450 MHz-6000 MHz 15, 30, 60 kHz FR2 24250 MHz-52600 MHz 60, 120, 240 kHz

As mentioned above, the numerical value of the frequency range of the NR system may be changed. For example, FR1 may include a frequency band of 410 MHz to 7125 MHz as shown in Table 2 below. That is, FR1 may include a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more. For example, a frequency band of 6 GHz (or 5850, 5900, 5925 MHz, etc.) or more included in FR1 may include an unlicensed band. Unlicensed bands may be used for a variety of purposes, for example for communication for vehicles (e.g., autonomous driving).

TABLE 2 Frequency Range Corresponding frequency designation range Subcarrier Spacing FR1  410 MHz-7125 MHz 15, 30, 60 kHz FR2 24250 MHz-52600 MHz 60, 120, 240 kHz

Here, the radio communication technologies implemented in the wireless devices in the present disclosure may include narrowband internet-of-things (NB-IoT) technology for low-power communication as well as LTE, NR and 6G. For example, NB-IoT technology may be an example of low power wide area network (LPWAN) technology, may be implemented in specifications such as LTE Cat NB1 and/or LTE Cat NB2, and may not be limited to the above-mentioned names. Additionally and/or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may communicate based on LTE-M technology. For example, LTE-M technology may be an example of LPWAN technology and be called by various names such as enhanced machine type communication (eMTC). For example, LTE-M technology may be implemented in at least one of the various specifications, such as 1) LTE Cat 0, 2) LTE Cat M1, 3) LTE Cat M2, 4) LTE non-bandwidth limited (non-BL), 5) LTE-MTC, 6) LTE Machine Type Communication, and/or 7) LTE M, and may not be limited to the above-mentioned names. Additionally and/or alternatively, the radio communication technologies implemented in the wireless devices in the present disclosure may include at least one of ZigBee, Bluetooth, and/or LPWAN which take into account low-power communication, and may not be limited to the above-mentioned names. For example, ZigBee technology may generate personal area networks (PANs) associated with small/low-power digital communication based on various specifications such as IEEE 802.15.4 and may be called various names.

FIG. 2 shows an example of wireless devices to which implementations of the present disclosure is applied.

Referring to FIG. 2, a first wireless device 100 and a second wireless device 200 may transmit/receive radio signals to/from an external device through a variety of RATs (e.g., LTE and NR).

In FIG. 2, {the first wireless device 100 and the second wireless device 200} may correspond to at least one of {the wireless device 100 a to 100 f and the BS 200}, {the wireless device 100 a to 100 f and the wireless device 100 a to 100 f} and/or {the BS 200 and the BS 200} of FIG. 1.

The first wireless device 100 may include at least one transceiver, such as a transceiver 106, at least one processing chip, such as a processing chip 101, and/or one or more antennas 108.

The processing chip 101 may include at least one processor, such a processor 102, and at least one memory, such as a memory 104. It is exemplarily shown in FIG. 2 that the memory 104 is included in the processing chip 101. Additional and/or alternatively, the memory 104 may be placed outside of the processing chip 101.

The processor 102 may control the memory 104 and/or the transceiver 106 and may be configured to implement the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts described in the present disclosure. For example, the processor 102 may process information within the memory 104 to generate first information/signals and then transmit radio signals including the first information/signals through the transceiver 106. The processor 102 may receive radio signals including second information/signals through the transceiver 106 and then store information obtained by processing the second information/signals in the memory 104.

The memory 104 may be operably connectable to the processor 102. The memory 104 may store various types of information and/or instructions. The memory 104 may store a software code 105 which implements instructions that, when executed by the processor 102, perform the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. For example, the software code 105 may implement instructions that, when executed by the processor 102, perform the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. For example, the software code 105 may control the processor 102 to perform one or more protocols. For example, the software code 105 may control the processor 102 to perform one or more layers of the radio interface protocol.

Herein, the processor 102 and the memory 104 may be a part of a communication modem/circuit/chip designed to implement RAT (e.g., LTE or NR). The transceiver 106 may be connected to the processor 102 and transmit and/or receive radio signals through one or more antennas 108. Each of the transceiver 106 may include a transmitter and/or a receiver. The transceiver 106 may be interchangeably used with radio frequency (RF) unit(s). In the present disclosure, the first wireless device 100 may represent a communication modem/circuit/chip.

The second wireless device 200 may include at least one transceiver, such as a transceiver 206, at least one processing chip, such as a processing chip 201, and/or one or more antennas 208.

The processing chip 201 may include at least one processor, such a processor 202, and at least one memory, such as a memory 204. It is exemplarily shown in FIG. 2 that the memory 204 is included in the processing chip 201. Additional and/or alternatively, the memory 204 may be placed outside of the processing chip 201.

The processor 202 may control the memory 204 and/or the transceiver 206 and may be configured to implement the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts described in the present disclosure. For example, the processor 202 may process information within the memory 204 to generate third information/signals and then transmit radio signals including the third information/signals through the transceiver 206. The processor 202 may receive radio signals including fourth information/signals through the transceiver 106 and then store information obtained by processing the fourth information/signals in the memory 204.

The memory 204 may be operably connectable to the processor 202. The memory 204 may store various types of information and/or instructions. The memory 204 may store a software code 205 which implements instructions that, when executed by the processor 202, perform the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. For example, the software code 205 may implement instructions that, when executed by the processor 202, perform the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. For example, the software code 205 may control the processor 202 to perform one or more protocols. For example, the software code 205 may control the processor 202 to perform one or more layers of the radio interface protocol.

Herein, the processor 202 and the memory 204 may be a part of a communication modem/circuit/chip designed to implement RAT (e.g., LTE or NR). The transceiver 206 may be connected to the processor 202 and transmit and/or receive radio signals through one or more antennas 208. Each of the transceiver 206 may include a transmitter and/or a receiver. The transceiver 206 may be interchangeably used with RF unit. In the present disclosure, the second wireless device 200 may represent a communication modem/circuit/chip.

Hereinafter, hardware elements of the wireless devices 100 and 200 will be described more specifically. One or more protocol layers may be implemented by, without being limited to, one or more processors 102 and 202. For example, the one or more processors 102 and 202 may implement one or more layers (e.g., functional layers such as physical (PHY) layer, media access control (MAC) layer, radio link control (RLC) layer, packet data convergence protocol (PDCP) layer, radio resource control (RRC) layer, and service data adaptation protocol (SDAP) layer). The one or more processors 102 and 202 may generate one or more protocol data units (PDUs) and/or one or more service data unit (SDUs) according to the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. The one or more processors 102 and 202 may generate messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. The one or more processors 102 and 202 may generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure and provide the generated signals to the one or more transceivers 106 and 206. The one or more processors 102 and 202 may receive the signals (e.g., baseband signals) from the one or more transceivers 106 and 206 and acquire the PDUs, SDUs, messages, control information, data, or information according to the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure.

The one or more processors 102 and 202 may be referred to as controllers, microcontrollers, microprocessors, or microcomputers. The one or more processors 102 and 202 may be implemented by hardware, firmware, software, or a combination thereof. As an example, one or more application specific integrated circuits (ASICs), one or more digital signal processors (DSPs), one or more digital signal processing devices (DSPDs), one or more programmable logic devices (PLDs), or one or more field programmable gate arrays (FPGAs) may be included in the one or more processors 102 and 202. The descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure may be implemented using firmware or software and the firmware or software may be configured to include the modules, procedures, or functions. Firmware or software configured to perform the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure may be included in the one or more processors 102 and 202 or stored in the one or more memories 104 and 204 so as to be driven by the one or more processors 102 and 202. The descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure may be implemented using firmware or software in the form of code, commands, and/or a set of commands.

The one or more memories 104 and 204 may be connected to the one or more processors 102 and 202 and store various types of data, signals, messages, information, programs, code, instructions, and/or commands. The one or more memories 104 and 204 may be configured by read-only memories (ROMs), random access memories (RAMs), electrically erasable programmable read-only memories (EPROMs), flash memories, hard drives, registers, cash memories, computer-readable storage media, and/or combinations thereof. The one or more memories 104 and 204 may be located at the interior and/or exterior of the one or more processors 102 and 202. The one or more memories 104 and 204 may be connected to the one or more processors 102 and 202 through various technologies such as wired or wireless connection.

The one or more transceivers 106 and 206 may transmit user data, control information, and/or radio signals/channels, mentioned in the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure, to one or more other devices. The one or more transceivers 106 and 206 may receive user data, control information, and/or radio signals/channels, mentioned in the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure, from one or more other devices. For example, the one or more transceivers 106 and 206 may be connected to the one or more processors 102 and 202 and transmit and receive radio signals. For example, the one or more processors 102 and 202 may perform control so that the one or more transceivers 106 and 206 may transmit user data, control information, or radio signals to one or more other devices. The one or more processors 102 and 202 may perform control so that the one or more transceivers 106 and 206 may receive user data, control information, or radio signals from one or more other devices.

The one or more transceivers 106 and 206 may be connected to the one or more antennas 108 and 208 and the one or more transceivers 106 and 206 may be configured to transmit and receive user data, control information, and/or radio signals/channels, mentioned in the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure, through the one or more antennas 108 and 208. In the present disclosure, the one or more antennas 108 and 208 may be a plurality of physical antennas or a plurality of logical antennas (e.g., antenna ports).

The one or more transceivers 106 and 206 may convert received user data, control information, radio signals/channels, etc., from RF band signals into baseband signals in order to process received user data, control information, radio signals/channels, etc., using the one or more processors 102 and 202. The one or more transceivers 106 and 206 may convert the user data, control information, radio signals/channels, etc., processed using the one or more processors 102 and 202 from the base band signals into the RF band signals. To this end, the one or more transceivers 106 and 206 may include (analog) oscillators and/or filters. For example, the one or more transceivers 106 and 206 can up-convert OFDM baseband signals to OFDM signals by their (analog) oscillators and/or filters under the control of the one or more processors 102 and 202 and transmit the up-converted OFDM signals at the carrier frequency. The one or more transceivers 106 and 206 may receive OFDM signals at a carrier frequency and down-convert the OFDM signals into OFDM baseband signals by their (analog) oscillators and/or filters under the control of the one or more processors 102 and 202.

In the implementations of the present disclosure, a UE may operate as a transmitting device in uplink (UL) and as a receiving device in downlink (DL). In the implementations of the present disclosure, a BS may operate as a receiving device in UL and as a transmitting device in DL. Hereinafter, for convenience of description, it is mainly assumed that the first wireless device 100 acts as the UE, and the second wireless device 200 acts as the BS. For example, the processor(s) 102 connected to, mounted on or launched in the first wireless device 100 may be configured to perform the UE behavior according to an implementation of the present disclosure or control the transceiver(s) 106 to perform the UE behavior according to an implementation of the present disclosure. The processor(s) 202 connected to, mounted on or launched in the second wireless device 200 may be configured to perform the BS behavior according to an implementation of the present disclosure or control the transceiver(s) 206 to perform the BS behavior according to an implementation of the present disclosure.

In the present disclosure, a BS is also referred to as a node B (NB), an eNode B (eNB), or a gNB.

FIG. 3 shows an example of a wireless device to which implementations of the present disclosure is applied.

The wireless device may be implemented in various forms according to a use-case/service (refer to FIG. 1).

Referring to FIG. 3, wireless devices 100 and 200 may correspond to the wireless devices 100 and 200 of FIG. 2 and may be configured by various elements, components, units/portions, and/or modules. For example, each of the wireless devices 100 and 200 may include a communication unit 110, a control unit 120, a memory unit 130, and additional components 140. The communication unit 110 may include a communication circuit 112 and transceiver(s) 114. For example, the communication circuit 112 may include the one or more processors 102 and 202 of FIG. 2 and/or the one or more memories 104 and 204 of FIG. 2. For example, the transceiver(s) 114 may include the one or more transceivers 106 and 206 of FIG. 2 and/or the one or more antennas 108 and 208 of FIG. 2. The control unit 120 is electrically connected to the communication unit 110, the memory unit 130, and the additional components 140 and controls overall operation of each of the wireless devices 100 and 200. For example, the control unit 120 may control an electric/mechanical operation of each of the wireless devices 100 and 200 based on programs/code/commands/information stored in the memory unit 130. The control unit 120 may transmit the information stored in the memory unit 130 to the exterior (e.g., other communication devices) via the communication unit 110 through a wireless/wired interface or store, in the memory unit 130, information received through the wireless/wired interface from the exterior (e.g., other communication devices) via the communication unit 110.

The additional components 140 may be variously configured according to types of the wireless devices 100 and 200. For example, the additional components 140 may include at least one of a power unit/battery, input/output (I/O) unit (e.g., audio I/O port, video I/O port), a driving unit, and a computing unit. The wireless devices 100 and 200 may be implemented in the form of, without being limited to, the robot (100 a of FIG. 1), the vehicles (100 b-1 and 100 b-2 of FIG. 1), the XR device (100 c of FIG. 1), the hand-held device (100 d of FIG. 1), the home appliance (100 e of FIG. 1), the IoT device (100 f of FIG. 1), a digital broadcast terminal, a hologram device, a public safety device, an MTC device, a medicine device, a FinTech device (or a finance device), a security device, a climate/environment device, the AI server/device (400 of FIG. 1), the BSs (200 of FIG. 1), a network node, etc. The wireless devices 100 and 200 may be used in a mobile or fixed place according to a use-example/service.

In FIG. 3, the entirety of the various elements, components, units/portions, and/or modules in the wireless devices 100 and 200 may be connected to each other through a wired interface or at least a part thereof may be wirelessly connected through the communication unit 110. For example, in each of the wireless devices 100 and 200, the control unit 120 and the communication unit 110 may be connected by wire and the control unit 120 and first units (e.g., 130 and 140) may be wirelessly connected through the communication unit 110. Each element, component, unit/portion, and/or module within the wireless devices 100 and 200 may further include one or more elements. For example, the control unit 120 may be configured by a set of one or more processors. As an example, the control unit 120 may be configured by a set of a communication control processor, an application processor (AP), an electronic control unit (ECU), a graphical processing unit, and a memory control processor. As another example, the memory unit 130 may be configured by a RAM, a DRAM, a ROM, a flash memory, a volatile memory, a non-volatile memory, and/or a combination thereof.

FIG. 4 shows an example of UE to which implementations of the present disclosure is applied.

Referring to FIG. 4, a UE 100 may correspond to the first wireless device 100 of FIG. 2 and/or the wireless device 100 or 200 of FIG. 3.

A UE 100 includes a processor 102, a memory 104, a transceiver 106, one or more antennas 108, a power management module 110, a battery 112, a display 114, a keypad 116, a subscriber identification module (SIM) card 118, a speaker 120, and a microphone 122.

The processor 102 may be configured to implement the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. The processor 102 may be configured to control one or more other components of the UE 100 to implement the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. Layers of the radio interface protocol may be implemented in the processor 102. The processor 102 may include ASIC, other chipset, logic circuit and/or data processing device. The processor 102 may be an application processor. The processor 102 may include at least one of a digital signal processor (DSP), a central processing unit (CPU), a graphics processing unit (GPU), a modem (modulator and demodulator). An example of the processor 102 may be found in SNAPDRAGON™ series of processors made by Qualcomm®, EXYNOS™ series of processors made by Samsung®, A series of processors made by Apple®, HELIO™ series of processors made by MediaTek®, ATOM™ series of processors made by Intel® or a corresponding next generation processor.

The memory 104 is operatively coupled with the processor 102 and stores a variety of information to operate the processor 102. The memory 104 may include ROM, RAM, flash memory, memory card, storage medium and/or other storage device. When the embodiments are implemented in software, the techniques described herein can be implemented with modules (e.g., procedures, functions, etc.) that perform the descriptions, functions, procedures, suggestions, methods and/or operational flowcharts disclosed in the present disclosure. The modules can be stored in the memory 104 and executed by the processor 102. The memory 104 can be implemented within the processor 102 or external to the processor 102 in which case those can be communicatively coupled to the processor 102 via various means as is known in the art.

The transceiver 106 is operatively coupled with the processor 102, and transmits and/or receives a radio signal. The transceiver 106 includes a transmitter and a receiver. The transceiver 106 may include baseband circuitry to process radio frequency signals. The transceiver 106 controls the one or more antennas 108 to transmit and/or receive a radio signal.

The power management module 110 manages power for the processor 102 and/or the transceiver 106. The battery 112 supplies power to the power management module 110.

The display 114 outputs results processed by the processor 102. The keypad 116 receives inputs to be used by the processor 102. The keypad 116 may be shown on the display 114.

The SIM card 118 is an integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key, which are used to identify and authenticate subscribers on mobile telephony devices (such as mobile phones and computers). It is also possible to store contact information on many SIM cards.

The speaker 120 outputs sound-related results processed by the processor 102. The microphone 122 receives sound-related inputs to be used by the processor 102.

FIG. 5 shows an example of 5G system architecture to which implementations of the present disclosure is applied.

The 5G system (5GS) architecture consists of the following network functions (NF).

-   -   Authentication Server Function (AUSF)     -   Access and Mobility Management Function (AMF)     -   Data Network (DN), e.g., operator services, Internet access or         3rd party services     -   Unstructured Data Storage Function (UDSF)     -   Network Exposure Function (NEF)     -   Intermediate NEF (I-NEF)     -   Network Repository Function (NRF)     -   Network Slice Selection Function (NSSF)     -   Policy Control Function (PCF)     -   Session Management Function (SMF)     -   Unified Data Management (UDM)     -   Unified Data Repository (UDR)     -   User Plane Function (UPF)     -   UE radio Capability Management Function (UCMF)     -   Application Function (AF)     -   User Equipment (UE)     -   (Radio) Access Network ((R)AN)     -   5G-Equipment Identity Register (5G-EIR)     -   Network Data Analytics Function (NWDAF)     -   CHarging Function (CHF)

Furthermore, the following network functions may be considered.

-   -   Non-3GPP InterWorking Function (N3IWF)     -   Trusted Non-3GPP Gateway Function (TNGF)     -   Wireline Access Gateway Function (W-AGF)

FIG. 5 depicts the 5G system architecture in the non-roaming case, using the reference point representation showing how various network functions interact with each other.

In FIG. 5, for the sake of clarity of the point-to-point diagrams, the UDSF, NEF and NRF have not been depicted. However, all depicted Network Functions can interact with the UDSF, UDR, NEF and NRF as necessary.

For clarity, the UDR and its connections with other NFs, e.g., PCF, are not depicted in FIG. 5. For clarity, the NWDAF and its connections with other NFs, e.g., PCF, are not depicted in FIG. 5.

The 5G system architecture contains the following reference points:

-   -   N1: Reference point between the UE and the AMF.     -   N2: Reference point between the (R)AN and the AMF.     -   N3: Reference point between the (R)AN and the UPF.     -   N4: Reference point between the SMF and the UPF.     -   N6: Reference point between the UPF and a Data Network.     -   N9: Reference point between two UPFs.

The following reference points show the interactions that exist between the NF services in the NFs.

-   -   N5: Reference point between the PCF and an AF.     -   N7: Reference point between the SMF and the PCF.     -   N8: Reference point between the UDM and the AMF.     -   N10: Reference point between the UDM and the SMF.     -   N11: Reference point between the AMF and the SMF.     -   N12: Reference point between the AMF and the AUSF.     -   N13: Reference point between the UDM and the AUSF.     -   N14: Reference point between two AMFs.     -   N15: Reference point between the PCF and the AMF in the case of         non-roaming scenario, PCF in the visited network and AMF in the         case of roaming scenario.     -   N16: Reference point between two SMFs, (in roaming case between         SMF in the visited network and the SMF in the home network).     -   N22: Reference point between the AMF and the NSSF.

In some cases, a couple of NFs may need to be associated with each other to serve a

UE.

A registration procedure is described. Section 4.2.2.2 of 3GPP TS 23.502 V16.3.0 (2019-12) can be referred.

FIGS. 6 and 7 show an example of a registration procedure to which implementations of the present disclosure is applied.

A UE needs to register with the network to get authorized to receive services, to enable mobility tracking and to enable reachability. The UE initiates the registration procedure using one of the following registration types:

-   -   Initial registration to the 5GS; or     -   Mobility registration update; or     -   Periodic registration update; or     -   Emergency registration.

The general registration procedure in FIGS. 6 and 7 applies on all these registration procedures, but the periodic registration update need not include all parameters that are used in other registration cases.

The general registration procedure in FIGS. 6 and 7 is also used for the case of registration in 3GPP access when the UE is already registered in a non-3GPP access, and vice versa. Registration in 3GPP access when the UE is already registered in a non-3GPP access scenario may require an AMF change.

First, procedures of FIG. 6 are described.

(1) Step 1: The UE transmits a Registration Request message to the (R)AN. The Registration Request message corresponds to AN message.

The Registration Request message may include AN parameters. In the case of NG-RAN, the AN parameters include, e.g., 5G SAE temporary mobile subscriber identity (SG-S-TMSI) or globally unique AMF ID (GUAMI), the selected public land mobile network (PLMN) ID (or PLMN ID and network identifier (NID)) and Requested network slice selection assistance information (NSSAI). The AN parameters also include establishment cause. The establishment cause provides the reason for requesting the establishment of an RRC connection. Whether and how the UE includes the Requested NSSAI as part of the AN parameters is dependent on the value of the access stratum connection establishment NSSAI inclusion mode parameter.

The Registration Request message may include a registration type. The registration type indicates if the UE wants to perform an initial registration (i.e., the UE is in RM-DEREGISTERED state), a mobility registration update (i.e., the UE is in RM-REGISTERED state and initiates a registration procedure due to mobility or due to the UE needs to update its capabilities or protocol parameters, or to request a change of the set of network slices it is allowed to use), a periodic registration update (i.e., the UE is in RM-REGISTERED state and initiates a registration procedure due to the periodic registration update timer expiry) or an emergency registration (i.e., the UE is in limited service state).

When the UE is performing an initial registration, the UE shall indicate its UE identity in the Registration Request message as follows, listed in decreasing order of preference:

i) a 5G globally unique temporary identifier (5G-GUTI) mapped from an evolved packet system (EPS) GUTI, if the UE has a valid EPS GUTI.

ii) a native 5G-GUTI assigned by the PLMN to which the UE is attempting to register, if available;

iii) a native 5G-GUTI assigned by an equivalent PLMN to the PLMN to which the UE is attempting to register, if available;

iv) a native 5G-GUTI assigned by any other PLMN, if available.

v) Otherwise, the UE shall include its subscriber concealed identifier (SUCI) in the Registration Request message.

When the UE performing an initial registration has both a valid EPS GUTI and a native 5G-GUTI, the UE shall also indicate the native 5G-GUTI as additional GUTI.

If more than one native 5G-GUTIs are available, the UE shall select the 5G-GUTI in decreasing order of preference among items (ii)-(iv) in the list above.

When the UE is performing an initial registration with a native 5G-GUTI, then the UE shall indicate the related GUAMI information in the AN parameters. When the UE is performing an initial registration with its SUCI, the UE shall not indicate any GUAMI information in the AN parameters.

For an emergency registration, the SUCI shall be included if the UE does not have a valid 5G-GUTI available; the permanent equipment identifier (PEI) shall be included when the UE has no subscriber permanent identifier (SUPI) and no valid 5G-GUTI. In other cases, the 5G-GUTI is included and it indicates the last serving AMF.

The Registration Request message may also include security parameters, PDU Session Status, etc. The security parameters are used for authentication and integrity protection. The PDU Session Status indicates the previously established PDU sessions in the UE. When the UE is connected to the two AMFs belonging to different PLMN via 3GPP access and non-3GPP access then the PDU Session status indicates the established PDU Session of the current PLMN in the UE.

(2) Step 2: The (R)AN selects an AMF.

If a 5G-S-TMSI or GUAMI is not included or the 5G-S-TMSI or GUAMI does not indicate a valid AMF, the (R)AN, based on (R)AT and requested NSSAI, if available, selects an AMF.

If UE is in CM-CONNECTED state, the (R)AN can forward the Registration Request message to the AMF based on the N2 connection of the UE.

If the (R)AN cannot select an appropriate AMF, it forwards the Registration Request message to an AMF which has been configured, in the (R)AN, to perform AMF selection.

(3) Step 3: The (R)AN transmits a Registration Request message to the new AMF. The Registration Request message corresponds to N2 message.

The Registration Request message may include whole information and/or a part of information included in the Registration Request message received from the UE which is described in step 1.

The Registration Request message may include N2 parameters. When NG-RAN is used, the N2 parameters include the selected PLMN ID (or PLMN ID and NID), location information and cell identity related to the cell in which the UE is camping, UE context request which indicates that a UE context including security information needs to be setup at the NG-RAN. When NG-RAN is used, the N2 parameters shall also include the establishment cause.

If the Registration type indicated by the UE is Periodic Registration Update, then steps 4 to 19 may be omitted.

(4) Step 4: If the UE's 5G-GUTI was included in the Registration Request message and the serving AMF has changed since last registration procedure, the new AMF may invoke the Namf_Communication_UEContextTransfer service operation on the old AMF including the complete registration request non-access stratum (NAS) message to request the UE's SUPI and UE context.

(5) Step 5: The Old AMF may respond to the new AMF for the Namf_Communication_UEContextTransfer invocation by including the UE's SUPI and UE context.

(6) Step 6: If the SUCI is not provided by the UE nor retrieved from the old AMF, the identity request procedure may be initiated by the new AMF sending the Identity Request message to the UE requesting the SUCI.

(7) Step 7: The UE may respond with an Identity Response message including the SUCI. The UE derives the SUCI by using the provisioned public key of the home PLMN (HPLMN).

(8) Step 8: The new AMF may decide to initiate UE authentication by invoking an AUSF. In that case, the new AMF selects an AUSF based on SUPI or SUCI.

(9) Step 9: Authentication/security may be established by the UE, new AMF, AUSF and/or UDM.

(10) Step 10: If the AMF has changed, the new AMF may notify the old AMF that the registration of the UE in the new AMF is completed by invoking the Namf_Communication_RegistrationCompleteNotify service operation. If the authentication/security procedure fails, then the registration shall be rejected, and the new AMF may invoke the Namf_Communication_RegistrationCompleteNotify service operation with a reject indication reason code towards the old AMF. The old AMF may continue as if the UE context transfer service operation was never received.

(11) Step 11: If the PEI was not provided by the UE nor retrieved from the old AMF, the Identity Request procedure may be initiated by the new AMF sending an Identity Request message to the UE to retrieve the PEI. The PEI shall be transferred encrypted unless the UE performs emergency registration and cannot be authenticated.

(12) Step 12: Optionally, the new AMF may initiate ME identity check by invoking the N5g-eir_EquipmentIdentityCheck_Get service operation.

Now, procedures of FIG. 7, which follow the procedures of FIG. 6, are described.

(13) Step 13: If step 14 below is to be performed, the new AMF, based on the SUPI, may select a UDM, then UDM may select a UDR instance.

(14) Step 14: The new AMF may register with the UDM.

(15) Step 15: The new AMF may select a PCF.

(16) Step 16: The new AMF may optionally perform an AM Policy Association

Establishment/Modification.

(17) Step 17: The new AMF may transmit Update/Release SM Context message (e.g., Nsmf_PDUSession_UpdateSMContext and/or Nsmf_PDUSession_ReleaseSMContext) to the SMF.

(18) Step 18: If the new AMF and the old AMF are in the same PLMN, the new AMF may send a UE Context Modification Request to the N3IWF/TNGF/W-AGF.

(19) Step 19: The N3IWF/TNGF/W-AGF may send a UE Context Modification Response to the new AMF.

(20) Step 20: After the new AMF receives the response message from the

N3IWF/TNGF/W-AGF in step 19, the new AMF may register with the UDM.

(21) Step 21: The new AMF transmits a Registration Accept message to the UE.

The new AMF sends a Registration Accept message to the UE indicating that the Registration Request has been accepted. 5G-GUTI is included if the new AMF allocates a new 5G-GUTI. If the UE is already in RM-REGISTERED state via another access in the same PLMN, the UE shall use the 5G-GUTI received in the Registration Accept message for both registrations. If no 5G-GUTI is included in the Registration Accept message, then the UE uses the 5G-GUTI assigned for the existing registration also for the new registration. If the new AMF allocates a new registration area, it shall send the registration area to the UE via Registration Accept message. If there is no registration area included in the Registration Accept message, the UE shall consider the old registration area as valid. Mobility Restrictions is included in case mobility restrictions applies for the UE and registration type is not emergency registration. The new AMF indicates the established PDU sessions to the UE in the PDU Session status. The UE removes locally any internal resources related to PDU sessions that are not marked as established in the received PDU Session status. When the UE is connected to the two AMFs belonging to different PLMN via 3GPP access and non-3GPP access then the UE removes locally any internal resources related to the PDU session of the current PLMN that are not marked as established in received PDU Session status. If the PDU Session status information was in the Registration Request message, the new AMF shall indicate the PDU Session status to the UE.

The Allowed NSSAI provided in the Registration Accept message is valid in the registration area and it applies for all the PLMNs which have their tracking areas included in the registration area. The Mapping Of Allowed NSSAI is the mapping of each S-NSSAI of the Allowed NSSAI to the HPLMN S-NSSAIs. The Mapping Of Configured NSSAI is the mapping of each S-NSSAI of the Configured NSSAI for the serving PLMN to the HPLMN S-NSSAIs.

Furthermore, optionally the new AMF performs a UE Policy Association Establishment.

(22) Step 22: The UE may send a Registration Complete message to the new AMF when it has successfully updated itself

The UE may send a Registration Complete message to the new AMF to acknowledge if a new 5G-GUTI was assigned.

(23) Step 23: For registration over 3GPP Access, if the new AMF does not release the signaling connection, the new AMF may send the RRC Inactive Assistance Information to the NG-RAN. For registration over non-3GPP Access, if the UE is also in CM-CONNECTED state on 3GPP access, the new AMF may send the RRC Inactive Assistance Information to the NG-RAN.

(24) Step 24: The new AMF may perform information update towards the UDM.

(25) Step 25: The UE may execute Network Slice-Specific Authentication and Authorization (NSSAA) procedure.

The network slicing information is information stored in the UE consisting of at least one of the followings.

a) default configured NSSAI

b) configured NSSAI for PLMN or stand-alone non-public network (SNPN)

c)S-NSSAI mapped to configured NSSAI for PLMN

d) pending NSSAI; and

e) for each access type:

1) allowed NSSAI for PLMN or SNPN; and

2) S-NSSAI mapped to allowed NSSAI for PLMN

Network slicing is described. Section 4.6 of 3GPP TS 24.501 V16.4.1 can be referred.

The 5GS supports network slicing. Within a PLMN or SNPN, a network slice is identified by an S-NSSAI, which is comprised of a slice/service type (SST) and a slice differentiator (SD). Inclusion of an SD in an S-NSSAI is optional. A set of one or more S-NSSAIs is called the NSSAI. The following NSSAIs may be defined.

a) configured NSSAI;

b) requested NSSAI;

c) allowed NSSAI;

d) subscribed S-NSSAIs; and

e) pending NSSAI.

The following NSSAIs may also be defined.

a) rejected NSSAI for the current PLMN or SNPN;

b) rejected NSSAI for the current registration area; and

c) rejected NSSAI for the failed or revoked NSSAA.

In case of a PLMN, a serving PLMN may configure a UE with the configured NSSAI per PLMN. In addition, the HPLMN may configure a UE with a single default configured NSSAI and consider the default configured NSSAI as valid in a PLMN for which the UE has neither a configured NSSAI nor an allowed NSSAI. In case of an SNPN, the SNPN may configure a UE with a configured NSSAI applicable to the SNPN.

The allowed NSSAI and rejected NSSAI for the current registration area are managed per access type independently, i.e., 3GPP access or non-3GPP access, and is applicable for the registration area. If the registration area contains tracking area IDs (TAIs) belonging to different PLMNs, which are equivalent PLMNs, the allowed NSSAI and the rejected NSSAI for the current registration area are applicable to these PLMNs in this registration area.

The allowed NSSAI that is associated with a registration area containing TAIs belonging to different PLMNs, which are equivalent PLMNs, can be used to form the requested NSSAI for any of the equivalent PLMNs when the UE is outside of the registration area where the allowed NSSAI was received.

When the NSSAA procedure is to be initiated for one or more S-NSSAIs in the requested NSSAI, these S-NSSAI(s) may be included in the pending NSSAI. When the NSSAA procedure is completed for an S-NSSAI that has been in the pending NSSAI, the S-NSSAI may be moved to the allowed NSSAI or rejected NSSAI depending on the outcome of the NSSAA procedure and communicated to the UE. The pending NSSAI is managed regardless of access type, i.e., the pending NSSAI is applicable to both 3GPP access and non-3GPP access even if sent over only one of the accesses.

The rejected NSSAI for the current PLMN or SNPN is applicable for the whole registered PLMN or SNPN. The AMF shall only send a rejected NSSAI for the current PLMN when the registration area consists of TAIs that only belong to the registered PLMN. If the UE receives a rejected NSSAI for the current PLMN, and the registration area also contains TAIs belonging to different PLMNs, the UE shall treat the received rejected NSSAI for the current PLMN as applicable to the whole registered PLMN.

The rejected NSSAI for the failed or revoked NSSAA includes one or more S-NSSAIs for which the NSSAA have been failed or revoked, and are applicable for the whole registered PLMN or SNPN.

Initial registration not accepted by the network is described. Section 5.5.1.2.5 of 3GPP TS 24.501 V16.4.1 can be referred.

When the network slice requested by the UE is not available, the network informs that a specific network slice is unavailable through a rejected NSSAI. When the network informs that a specific slice is unavailable, the UE performs the registration procedure again in the current cell if a network slice other than the specific network slice is available, and selects another PLMN if all network slices are unavailable.

More specifically, if the initial registration request cannot be accepted by the network, the AMF shall send a REGISTRATION REJECT message to the UE including an appropriate SGMM cause value.

If the initial registration request is rejected for the following reason, the network shall set the SGMM cause value to #62 “No network slices available” and may include the rejected NSSAI.

a) all the S-NSSAI(s) included in the requested NSSAI are either rejected for the current PLMN, rejected for the current registration area, or rejected due to the failed or revoked NSSAA, or the UE did not request any S-NSSAIs; and

b-1) the UE set the NSSAA bit in the SGMM capability information element (IE) to “Network slice-specific authentication and authorization supported” and there are no subscribed S-NSSAIs marked as default; or

b-2) the UE set the NSSAA bit in the SGMM capability information element (IE) to “Network slice-specific authentication and authorization not supported”, and i) there are no subscribed S-NSSAIs which are marked as default, ii) all subscribed S-NSSAIs marked as default are subject to NSSAA;

The UE performs the following operation according to the SGMM cause value set to #62.

The UE shall abort the initial registration procedure, set the 5GS update status to “5U2 NOT UPDATED” and enter state “SGMM-DEREGISTERED.NORMAL-SERVICE” or “SGMM-DEREGISTERED.PLMN-SEARCH”. Additionally, the UE shall reset the registration attempt counter.

The UE receiving the rejected NSSAI in the REGISTRATION REJECT message takes the following actions based on the rejection cause in the rejected S-NSSAI(s).

-   -   “S-NSSAI not available in the current PLMN or SNPN”: The UE         shall store the rejected S-NSSAI(s) in the rejected NSSAI for         the current PLMN or SNPN and not attempt to use this S-NSSAI(s)         in the current PLMN or SNPN until switching off the UE, the         universal integrated circuit card (UICC) containing the         universal subscriber identification module (USIM) is removed, an         entry of the “list of subscriber data” with the SNPN identity of         the current SNPN is updated, or the rejected S-NSSAI(s) are         removed.     -   “S-NSSAI not available in the current registration area”: The UE         shall store the rejected S-NSSAI(s) in the rejected NSSAI for         the current registration area and not attempt to use this         S-NSSAI(s) in the current registration area until switching off         the UE, the UE leaves the current registration area, the UICC         containing the USIM is removed, an entry of the “list of         subscriber data” with the SNPN identity of the current SNPN is         updated, or the rejected S-NSSAI(s) are removed.     -   “S-NSSAI not available due to the failed or revoked network         slice-specific authentication and authorization”: The UE shall         store the rejected S-NSSAI(s) in the rejected NSSAI due to the         failed or revoked NSSAA and not attempt to use this S-NSSAI(s)         in the current PLMN through all accesses until switching off the         UE, the UICC containing the USIM is removed, an entry of the         “list of subscriber data” with the SNPN identity of the current         SNPN is updated, or the rejected S-NSSAI(s) are removed.

If the UE has an allowed NSSAI or configured NSSAI that contains S-NSSAI(s) which are not included any of the rejected NSSAI for the current PLMN or SNPN, the rejected NSSAI for the current registration area, and the rejected NSSAI due to the failed or revoked NSSAA, the UE may stay in the current serving cell, and apply the normal cell reselection process. In addition, the UE may start an initial registration with a requested NSSAI that includes any S-NSSAI from the allowed NSSAI or the configured NSSAI that is neither in the rejected NSSAI for the PLMN or SNPN nor in the rejected NSSAI for the current registration area. Otherwise, the UE may perform a PLMN selection or SNPN selection.

NSSAI storage is described. Section 4.6.2.2 of 3GPP TS 24.501 V16.4.1 can be referred.

In general, the configured NSSAI is the subscription NSSAI of the UE when the UE accesses the HPLMN, and continues to be the same as long as the subscriber information of the UE does not change. However, an existing S-NSSAI may be created as a configured NSSAI due to a change in subscriber information, etc., or a specific S-NSSAI may be removed. Thereafter, the AMF may inform the UE of the updated S-NSSAI to the current access network.

In addition, the UE may store and store the NSSAI configured for the network visited by the UE in the non-volatile memory. Therefore, when the UE selects a new VPLMN, there may be NSSAI information configured in the previously visited network. Therefore, when performing PLMN selection, the UE may have the configured NSSAI information of the PLMN selected by the UE.

In addition, if there is a service level agreement (SLA) between the HPLMN and the VPLMN to which the UE can access, the UE can know of which HPLMN the VPLMN has the S-NSSAI.

If available, the configured NSSAI(s) shall be stored in a non-volatile memory in the UE. The allowed NSSAI(s) should be stored in a non-volatile memory in the UE.

Each of the configured NSSAI stored in the UE is a set composed of at most 16 S-NSSAIs. Each of the allowed NSSAI stored in the UE is a set composed of at most 8 S-NSSAIs and is associated with a PLMN ID or SNPN ID and an access type. Each of the configured NSSAI except the default configured NSSAI, and the rejected NSSAI is associated with a PLMN ID or SNPN ID. The S-NSSAI(s) in the rejected NSSAI for the current registration area are further associated with a registration area where the rejected S-NSSAI(s) is not available. The S-NSSAI(s) in the rejected NSSAI for the current PLMN or SNPN shall be considered rejected for the current PLMN or SNPN regardless of the access type. The S-NSSAI(s) in the rejected NSSAI for the failed or revoked NSSAA shall be considered rejected for the current PLMN regardless of the access type. There shall be no duplicated PLMN IDs or SNPN IDs in each of the list of configured NSSAI(s), allowed NSSAI(s), rejected NSSAI(s) for the current PLMN or SNPN, and rejected NSSAI(s) for the current registration area.

The UE stores NSSAIs as follows.

a) The configured NSSAI shall be stored until a new configured NSSAI is received for a given PLMN or SNPN. The network may provide to the UE the mapped S-NSSAI(s) for the new configured NSSAI which shall also be stored in the UE. When the UE is provisioned with a new configured NSSAI for a PLMN or SNPN, the UE shall perform the followings.

1) replace any stored configured NSSAI for this PLMN or SNPN with the new configured NSSAI for this PLMN or SNPN;

2) delete any stored mapped S-NSSAI(s) for the configured NSSAI and, if available, store the mapped S-NSSAI(s) for the new configured NSSAI;

3) delete any stored allowed NSSAI for this PLMN or SNPN and, if available, the stored mapped S-NSSAI(s) for the allowed NSSAI, if the UE received the new configured NSSAI for this PLMN or SNPN and the Configuration update indication IE with the Registration requested bit set to “registration requested”, in the same CONFIGURATION UPDATE COMMAND message but without any new allowed NSSAI for this PLMN or SNPN included; and

4) delete any stored rejected NSSAI for the current PLMN or SNPN, rejected NSSAI for the current registration area and rejected NSSAI for the failed or revoked NSSAA.

If the UE receives an S-NSSAI associated with a PLMN ID from the network during the PDN connection establishment procedure in EPS, the UE may store the received S-NSSAI in the configured NSSAI for the PLMN identified by the PLMN ID associated with the S-NSSAI (if not already in the configured NSSAI).

The UE may continue storing a received configured NSSAI for a PLMN and associated mapped S-NSSAI(s), if available, when the UE registers in another PLMN.

b) The allowed NSSAI shall be stored until a new allowed NSSAI is received for a given PLMN or SNPN. The network may provide to the UE the mapped S-NSSAI(s) for the new allowed NSSAI which shall also be stored in the UE. When a new allowed NSSAI for a PLMN or SNPN is received, the UE shall perform the followings.

1) replace any stored allowed NSSAI for this PLMN or SNPN with the new allowed

NSSAI for this PLMN or SNPN;

2) delete any stored mapped S-NSSAI(s) for the allowed NSSAI and, if available, store the mapped S-NSSAI(s) for the new allowed NSSAI;

3) remove from the stored rejected NSSAI, the S-NSSAI(s), if any, included in the new allowed NSSAI for the current PLMN or SNPN; and

4) remove from the stored pending NSSAI, one or more S-NSSAIs, if any, included in the new allowed NSSAI for the current PLMN or SNPN.

If the UE receives the CONFIGURATION UPDATE COMMAND message with the Registration requested bit of the Configuration update indication IE set to “registration requested” and contains no other parameters, the UE shall delete any stored allowed NSSAI for this PLMN or SNPN, and delete any stored mapped S-NSSAI(s) for the allowed NSSAI, if available.

c) When the UE receives the S-NSSAI(s) included in rejected NSSAI in the REGISTRATION ACCEPT message, the REGISTRATION REJECT message, the DEREGISTRATION REQUEST message or in the CONFIGURATION UPDATE COMMAND message, the UE shall perform the followings.

1) store the S-NSSAI(s) into the rejected NSSAI based on the associated rejection cause(s);

2) remove from the stored allowed NSSAI for the current PLMN or SNPN, the 5-NSSAI(s), if any, included in the:

i) rejected NSSAI for the current PLMN or SNPN, for each and every access type;

ii) rejected NSSAI for the current registration area, associated with the same access type; and

iii) rejected NSSAI due to the failed or revoked NSSAA, for each and every access type;

3) remove from the stored pending NSSAI for the current PLMN or SNPN, one or more S-NSSAIs, if any, included in the:

i) rejected NSSAI for the current PLMN or SNPN, for each and every access type;

ii) rejected NSSAI for the current registration area, associated with the same access type; and

iii) rejected NSSAI for the failed or revoked NSSAA, for each and every access type.

When the UE:

1) deregisters with the current PLMN using explicit signalling or enters state SGMM-DEREGISTERED for the current PLMN; or

2) successfully registers with a new PLMN; or

3) enters state SGMM-DEREGISTERED following an unsuccessful registration with a new PLMN;

and the UE is not registered with the current PLMN over another access, the rejected NSSAI for the current PLMN shall be deleted.

When the UE:

1) deregisters over an access type;

2) successfully registers in a new registration area over an access type; or

3) enters state SGMM-DEREGISTERED or SGMM-REGISTERED following an unsuccessful registration in a new registration area over an access type;

the rejected NSSAI for the current registration area corresponding to the access type shall be deleted.

d) When the UE receives one or more S-NSSAIs included in pending NSSAI in the REGISTRATION ACCEPT message, the UE shall store one or more S-NSSAIs for the pending NSSAI.

When the UE:

1) deregisters with the current PLMN using explicit signalling or enters state SGMM-DEREGISTERED for the current PLMN;

2) successfully registers with a new PLMN;

3) enters state SGMM-DEREGISTERED following an unsuccessful registration with a new PLMN;

4) successfully completes an attach or tracking area update procedure in S1 mode; or

5) initiates attach or tracking area update procedure in S1 mode and receives an ATTACH REJECT or TRACKING AREA UPDATE REJECT;

and the UE is not registered with the current PLMN over another access, the pending NSSAI for the current PLMN shall be deleted.

e) In case of a PLMN, when the UE receives the Network slicing indication IE with the Network slicing subscription change indication set to “Network slicing subscription changed” in the REGISTRATION ACCEPT message or in the CONFIGURATION UPDATE COMMAND message, the UE shall delete the network slicing information for each of the PLMNs that the UE has slicing information stored for (excluding the current PLMN). The UE shall not delete the default configured NSSAI. Additionally, the UE shall update the network slicing information for the current PLMN (if received) as specified above in bullets a), b), c) and e).

NSSAA is described. Section 4.2.9 of 3GPP TS 23.502 V16.4.0 can be referred.

The NSSAA procedure is triggered for an S-NSSAI requiring Network Slice-Specific Authentication and Authorization with an AAA server (AAA-S) which may be hosted by the H-PLMN operator or by a third party which has a business relationship with the H-PLMN, using the EAP framework. An AAA proxy (AAA-P) in the HPLMN may be involved, e.g., if the AAA Server belongs to a third party.

This procedure is triggered by the AMF during a Registration procedure (e.g., Step 25 of FIG. 7) when some Network Slices require Slice-Specific Authentication and Authorization, when AMF determines that Network Slice-Specific Authentication and Authorization is required for an S-NSSAI in the current Allowed NSSAI (e.g., subscription change), or when the AAA server that authenticated the Network Slice triggers a re-authentication.

The AMF performs the role of the EAP authenticator and communicates with the AAA-S via the AUSF. The AUSF undertakes any AAA protocol interworking with the AAA protocol supported by the AAA-S.

If the NSSAA procedure fails for all S-NSSAIs (if any) in the existing Allowed NSSAI for the UE and (if any) for all S-NSSAIs in the Requested NSSAI, the AMF shall execute the network-initiated deregistration procedure, or reject the UE Registration Request (if that was the trigger for this procedure), and it shall include in the explicit De-Registration Request or Registration Reject message the list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value. If the Network Slice-Specific Re-Authentication and Re-Authorization fails and there are PDU session(s) established that are associated with the S-NSSAI for which the NSSAA procedure failed, the AMF shall initiate the PDU Session Release procedure to release the PDU sessions with the appropriate cause value.

In the AAA server triggered Network Slice Specific Authorization Revocation procedure, the AAA-S requests the revocation of authorization for the Network Slice specified by the S-NSSAI in the AAA protocol Revoke Auth Request message.

The AMF updates the UE configuration to revoke the S-NSSAI from the current Allowed NSSAI, for any Access Type for which NSSAA had been successfully run on this S-NSSAI. The UE Configuration Update may include a request to Register if the AMF needs to be re-allocated. The AMF provides a new Allowed NSSAI to the UE by removing the S-NSSAI for which authorization has been revoked. The AMF provides new rejected NSSAIs to the UE including the S-NSSAI for which authorization has been revoked. If no S-NSSAI is left in Allowed NSSAI for an access after the revocation, and a Default NSSAI exists that requires no Network Slice Specific Authentication or for which a Network Slice Specific Authentication did not previously fail over this access, then the AMF may provide a new Allowed NSSAI to the UE containing the Default NSSAI. If no S-NSSAI is left in Allowed NSSAI for an access after the revocation, and no Default NSSAI can be provided to the UE in the Allowed NSSAI or a previous Network Slice Specific Authentication failed for the Default NSSAI over this access, then the AMF shall execute the Network-initiated Deregistration procedure for the access, and it shall include in the explicit De-Registration Request message the list of Rejected S-NSSAIs, each of them with the appropriate rejection cause value. If there are PDU session(s) established that are associated with the revoked S-NSSAI, the AMF shall initiate the PDU Session Release procedure to release the PDU sessions with the appropriate cause value.

PLMN selection is described. Section 5.4.5 of 3GPP TS 24.501 V16.4.1 or Section 4.4.3.3 of 3GPP TS 23.122 V16.3.0 can be referred.

The NAS transport procedure can handle steering of roaming (SOR). When the network informs the “SOR transparent container” in the payload container, the UE may replace the PLMN information informed by the network with the value of the PLMN with the highest priority of the USIM's “operator controlled PLMN selector with access technology”. Therefore, when the UE performs PLMN selection, the UE may first find the corresponding PLMN received from the network.

When the UE performs PLMN selection in the VPLMN, it may periodically find a PLMN of high priority. At this time, the UE may find a PLMN of high priority within an HPLMN, an equivalent HPLMN (EHPLMN), a user controlled PLMN selector, or operator controlled PLMN selector.

Summarizing the above description, the NSSAA procedure and NSSAA failure/revoke apply to the S-NSSAI of the HPLMN, not the S-NSSAI of the current PLMN. In addition, when the network informs the UE of the failure of using the corresponding network slice due to NSSAA failure in the VPLMN, the UE performs the PLMN selection again to find a transmittable network if there is no S-NSSAI that can be transmitted in the current network.

If the NSSAA procedure for which the previous failure occurred for all S-NSSAIs that can be transmitted is performed in the newly selected PLMN, even if a new PLMN is selected, NSSAA failure may occur again for all S-NSSAIs, and the problem of repeating PLMN selection may occur.

That is, in a roaming environment, when NSSAA fails, in order to perform efficient PLMN selection, the UE performs PLMN selection only for PLMNs having the S-NSSAI that can be transmitted by excluding the PLMN having the S-NSSAI for which the NSSAA fails using the information of the UE. Currently, in a method for the UE to determine the S-NSSAI that can be transmitted, if there is an S-NSSAI that belongs to the allowed NSSAI or the configured NSSAI that the UE has and is not included in the rejected NSSAI, the UE considers that data transmission is possible through the current network, and does not perform new PLMN selection. However, there are cases where the default configured NSSAI does not exist in the configured NSSAI, and in this case, the UE unnecessarily selects a new PLMN despite data transmission is possible in the current network based on the default configured NSSAI.

FIG. 8 shows an example of a situation to which the implementation of the present disclosure is applied.

Referring to FIG. 8, the HPLMN of the UE has three network slices (i.e., GM V2X slice, URLLC slice, VW V2X slice). The NSSAA procedure is performed for all three network slices. It is assumed that NSSAA failed for GM V2X slice and URLLC slice among three network slices, and NSSAA succeeded for VW V2X slice.

Meanwhile, it is also assumed that the UE is currently in a roaming state and that VPLMN #1, VPLMN #2, and VPLMN #3 exist as accessible networks. The NSSAI configured for each VPLMN may be different. That is, in FIG. 8, the configured NSSAI of VPLMN #1 is a GM V2X slice and a URLLC slice, the configured NSSAI of VPLMN #2 is a VW V2X slice and a URLLC slice, and the configured NSSAI of VPLMN #3 is a GM V2X slice.

According to the current NSSAA procedure, if the network to which the UE first selects and tries to access among the roaming networks is VPLMN #1, since the NSSAA for the configured NSSAI (i.e., GM V2X slice and URLLC slice) of VPLMN #1 has already failed in HPLMN, VPLMN #1 informs that all S-NSSAI of the configured NSSAI is a rejected NSSAI, and informs the access failure. Afterwards, the UE may select VPLMN #3 by performing PLMN selection again. When the UE selects VPLMN #3 and attempts to access, since the NSSAA for the configured NSSAI (i.e., GM V2X slice) of VPLMN #3 has also already failed in HPLMN, VPLMN #3 informs that all S-NSSAI of the configured NSSAI is a rejected NSSAI, and informs the access failure. Afterwards, the UE may select VPLMN #2 by performing PLMN selection again. When the UE selects VPLMN #2 and attempts to access, since the NSSAA for the configured NSSAI (i.e., VW V2X slice) of VPLMN #2 succeeded in HPLMN, only then can the access of the UE succeed.

That is, when NSSAA fails in the roaming network, an unnecessary process of selecting an unnecessary VPLMN and attempting to access the corresponding VPLMN, receiving notification of access failure from the corresponding VPLMN, and performing PLMN selection again may be performed. Therefore, a method for efficiently performing PLMN selection may be required.

According to implementations of the present disclosure, in the roaming environment, in the case of NSSAA failure, in order to perform efficient PLMN selection, a method of excluding PLMNs having S-NSSAI for which NSSAA has failed using information stored by the UE, and performing PLMN selection only for PLMNs having S-NSSAI that can be transmitted is provided.

According to implementations of the present disclosure, a new method for a UE to select S-NSSAI that can be transmitted is provided.

According to implementations of the present disclosure, a method for the UE to determine a PLMN having S-NSSAI for which NSSAA has failed using the stored information, to exclude the determined PLMN from candidates for PLMN selection, and to perform PLMN selection only for a PLMN having S-NSSAI that can be transmitted is provided.

According to implementations of the present disclosure, a method is provided in which the network determines S-NSSAI for which the NSSAA fails, excludes the PLMNs corresponding to the S-NSSAI for which the NSSAA has failed and informs the UE of the available PLMNs. Accordingly, there is provided a method in which the UE performs PLMN selection using the available PLMN notified by the network.

Various implementations and/or embodiments of the present disclosure to be described below may be performed individually, or two or more may be combined and performed complexly.

The following drawings are created to explain specific embodiments of the present disclosure. The names of the specific devices or the names of the specific signals/messages/fields shown in the drawings are provided by way of example, and thus the technical features of the present disclosure are not limited to the specific names used in the following drawings.

1. First Implementation

FIG. 9 shows an example of a method performed by a UE to which the first implementation of the present disclosure is applied.

In step S900, the UE obtains default configured NSSAI which can be used in a first PLMN.

In some implementations, the default NSSAI may be valid in a PLMN where the UE does not have the allowed NSSAI and the configured NSSAI.

In some implementations, the default NSSAI may be obtained from a HPLMN.

In step S910, the UE generates first requested NSSAI including a first S-NSSAI corresponding to a network slice to which the UE requests to register with.

In step S920, the UE transmits, to an AMF of the first PLMN, a first registration request message including the first requested NSSAI.

In step S930, the UE receives, from the AMF of the first PLMN, a registration reject message in response to the first registration request message. The registration reject message includes rejected NSSAI including the first S-NSSAI, and the registration reject message includes a cause value #62 for the rejected NSSAI. The cause value #62 indicates “No network slices available”.

In step S940, based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with, the UE generates second NSSAI including the second S-NSSAI, and transmits, to the AMF of the first PLMN, a second registration request message including the second requested NSSAI.

In some implementations, the UE may not have the allowed NSSAI and the configured NSSAI for the first PLMN. The UE not having the allowed NSSAI and the configured NSSAI for the first PLMN may comprise removing the first S-NSSAI included in the rejected NSSAI from the allowed NSSAI for the first PLMN and/or the configured NSSAI for the first PLMN.

In some implementations, the allowed NSSAI may be obtained from the AMF of the first PLMN through a registration accept message for the first PLMN. In some implementations, the configured NSSAI may be configured by the first PLMN.

In some implementations, the second registration request message may be transmitted without PLMN selection.

In some implementations, the UE may communicate with at least one of a mobile device, a network and/or an autonomous vehicle other than the UE.

Furthermore, the method in perspective of the UE described above in FIG. 9 may be performed by the first wireless device 100 shown in FIG. 2, the wireless device 100 shown in FIG. 3, and/or the UE 100 shown in FIG. 4.

More specifically, the UE comprises at least one transceiver, at least one processor, and at least one memory operably connectable to the at least one processor. The at least one memory stores instructions that, based on being executed by the at least one processor, perform operations below.

The operations comprise obtaining default configured NSSAI which can be used in a first PLMN.

In some implementations, the default NSSAI may be valid in a PLMN where the UE does not have the allowed NSSAI and the configured NSSAI.

In some implementations, the default NSSAI may be obtained from a HPLMN.

The operations comprise generating first requested NSSAI including a first S-NSSAI corresponding to a network slice to which the UE requests to register with.

The operations comprise transmitting, to an AMF of the first PLMN, a first registration request message including the first requested NSSAI.

The operations comprise receiving, from the AMF of the first PLMN, a registration reject message in response to the first registration request message. The registration reject message includes rejected NSSAI including the first S-NSSAI, and the registration reject message includes a cause value #62 for the rejected NSSAI. The cause value #62 indicates “No network slices available”.

Based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with, the operations comprise generating second NSSAI including the second S-NSSAI, and transmitting, to the AMF of the first PLMN, a second registration request message including the second requested NSSAI.

In some implementations, the UE may not have the allowed NSSAI and the configured NSSAI for the first PLMN. The UE not having the allowed NSSAI and the configured NSSAI for the first PLMN may comprise removing the first S-NSSAI included in the rejected NSSAI from the allowed NSSAI for the first PLMN and/or the configured NSSAI for the first PLMN.

In some implementations, the allowed NSSAI may be obtained from the AMF of the first PLMN through a registration accept message for the first PLMN. In some implementations, the configured NSSAI may be configured by the first PLMN.

In some implementations, the second registration request message may be transmitted without PLMN selection.

Furthermore, the method in perspective of the UE described above in FIG. 9 may be performed by control of the processor 102 included in the first wireless device 100 shown in FIG. 2, by control of the communication unit 110 and/or the control unit 120 included in the wireless device 100 shown in FIG. 3, and/or by control of the processor 102 included in the UE 100 shown in FIG. 4.

More specifically, an apparatus operating in a wireless communication system comprises at least one processor, and at least one memory operably connectable to the at least one processor. The at least one processor is configured to perform operations comprising: obtaining default configured NSSAI which can be used in a first PLMN, generating first requested NSSAI including a first S-NSSAI corresponding to a network slice to which the UE requests to register with, generating a first registration request message including the first requested NSSAI, obtaining a registration reject message in response to the first registration request message, wherein the registration reject message includes rejected NSSAI including the first S-NSSAI, wherein the registration reject message includes a cause value #62 for the rejected NSSAI, based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with: generating second NSSAI including the second S-NSSAI, generating a second registration request message including the second requested NSSAI.

Furthermore, the method in perspective of the UE described above in FIG. 9 may be performed by a software code 105 stored in the memory 104 included in the first wireless device 100 shown in FIG. 2.

The technical features of the present disclosure may be embodied directly in hardware, in a software executed by a processor, or in a combination of the two. For example, a method performed by a wireless device in a wireless communication may be implemented in hardware, software, firmware, or any combination thereof. For example, a software may reside in RAM, flash memory, ROM, EPROM, EEPROM, registers, hard disk, a removable disk, a CD-ROM, or any other storage medium.

Some example of storage medium may be coupled to the processor such that the processor can read information from the storage medium. In the alternative, the storage medium may be integral to the processor. The processor and the storage medium may reside in an ASIC. For other example, the processor and the storage medium may reside as discrete components.

The computer-readable medium may include a tangible and non-transitory computer-readable storage medium.

For example, non-transitory computer-readable media may include RAM such as synchronous dynamic random access memory (SDRAM), ROM, non-volatile random access memory (NVRAM), EEPROM, flash memory, magnetic or optical data storage media, or any other medium that can be used to store instructions or data structures. Non-transitory computer-readable media may also include combinations of the above.

In addition, the method described herein may be realized at least in part by a computer-readable communication medium that carries or communicates code in the form of instructions or data structures and that can be accessed, read, and/or executed by a computer.

According to some implementations of the present disclosure, a non-transitory computer-readable medium (CRM) has stored thereon a plurality of instructions.

More specifically, at least one CRM stores instructions that, based on being executed by at least one processor, perform operations comprising: obtaining default configured NSSAI which can be used in a first PLMN, generating first requested NSSAI including a first S-NSSAI corresponding to a network slice to which the UE requests to register with, generating a first registration request message including the first requested NSSAI, obtaining a registration reject message in response to the first registration request message, wherein the registration reject message includes rejected NSSAI including the first S-NSSAI, wherein the registration reject message includes a cause value #62 for the rejected NSSAI, based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with: generating second NSSAI including the second S-NSSAI, generating a second registration request message including the second requested NSSAI.

According to the first implementation of the present disclosure, when the UE receives from the network that a specific network slice is not available (i.e., when the cause value #62 is received), as a method for the UE to determine S-NSSAI that can be transmitted, if there is any S-NSSAI that is not included in the rejected NSSAI among the default configured NSSAI as well as the allowed NSSAI and the configured NSSAI possessed by the UE, the UE determines that data transmission is possible through the current network, and the PLMN selection may not be performed.

According to the first implementation of the present disclosure, as an operation when the UE receives the cause value #62, the UE may also generate the requested NSSAI based on the default configured NSSAI. At this time, in order to prevent the UE from requesting S-NSSAI that is not supported by the serving PLMN in a general situation, the UE may generate the requested NSSAI based on the default configured NSSAI only when all of the requested NSSAIs generated based on the allowed NSSAI and/or the configured NSSAI are rejected. Specifically, when all S-NSSAIs included in the request NSSAI generated based on the allowed NSSAI and/or the configured NSSAI are rejected by the network, so the corresponding S-NSSAI is included in the rejected NSSAI, and accordingly, the S-NSSAI included in the rejected NSSAI is deleted from the allowed NSSAI and/or configured NSSAI, so that the UE does not have the allowed NSSAI and/or the rejected NSSAI, the UE may generate the requested NSSAI based on the default configured NSSAI.

According to the first implementation of the present disclosure, as an operation when the UE receives the cause value #62, if the UE has neither allowed NSSAI for the current PLMN or SNPN nor configured NSSAI for the current PLMN and has a default configured NSSAI containing one or more S-NSSAIs that are not included in any of the rejected NSSAI for the PLMN or SNPN, the rejected NSSAI for the current registration area, and the rejected NSSAI for the failed or revoked NSSAA, the UE may stay in the current serving cell, apply the normal cell reselection process, and start an initial registration by generating a requested NSSAI based on that default configured NSSAI. Otherwise, the UE may perform a PLMN selection or SNPN selection.

According to the first implementation of the present disclosure, as the operation when the UE receives the cause value #62, if the UE has an allowed NSSAI or configured NSSAI or default configured NSSAI that contains S-NSSAI(s) which are not included any of the rejected NSSAI for the current PLMN or SNPN, the rejected NSSAI for the current registration area, and the rejected NSSAI for the failed or revoked NSSAA, the UE may stay in the current serving cell, apply the normal cell reselection process. Furthermore, the UE may start an initial registration with a requested NSSAI that includes any S-NSSAI from the allowed NSSAI or the configured NSSAI or default configured NSSAI that is neither in the rejected NSSAI for the PLMN or SNPN nor in the rejected NSSAI for the current registration area nor in the rejected NSSAI for the failed or revoked NSSAA. Otherwise, the UE may perform a PLMN selection or SNPN selection.

According to the first implementation of the present disclosure, the requested NSSAI may be any one of the following.

-   -   the default configured NSSAI or configured-NSSAI, or a subset         thereof, e.g., if the

UE has no allowed NSSAI for the access type for the serving PLMN;

-   -   the allowed-NSSAI for the access type over which the requested         NSSAI is sent, or a subset thereof; or     -   the allowed-NSSAI for the access type over which the requested         NSSAI is sent, or a subset thereof, +one or more S-NSSAIs from         the configured-NSSAI not yet in the allowed NSSAI for the access         type.

According to the first implementation of the present disclosure, the requested NSSAI may be any one of the following.

-   -   the default configured NSSAI, i.e., if the UE has no configured         NSSAI nor an allowed NSSAI for the serving PLMN or if the UE has         failed to get allowed NSSAI based on configured NSSAI;     -   configured-NSSAI, or a subset thereof, e.g., if the UE has no         allowed NSSAI for the access type for the serving PLMN;     -   the allowed-NSSAI for the access type over which the requested         NSSAI is sent, or a subset thereof; or     -   the allowed-NSSAI for the access type over which the requested         NSSAI is sent, or a subset thereof, +one or more S-NSSAIs from         the configured-NSSAI not yet in the allowed NSSAI for the access         type.

When the UE generates and/or updates the requested NSSAI based on the default configured NSSAI, the UE may indicate that the requested NSSAI has been generated and/or updated based on the default configured NSSAI. This is because the network does not provide a configured NSSAI, but the UE may have a default configured NSSAI.

According to the first implementation of the present disclosure, by determining the S-NSSAI that can be transmitted based on the default configured NSSAI, unnecessary PLMN selection procedure and registration procedure can be efficiently removed.

2. Second Implementation

According to the second implementation of the present disclosure, the UE may determine the PLMN with the S-NSSAI that has failed NSSAA using the information of the UE, may exclude the determined PLMN from the PLMN selection, and may perform PLMN selection only for PLMNs with S-NSSAI that can be transmitted. The information of the UE may be NSSAI stored in non-volatile memory. The NSSAI may include a configured NSSAI. The NSSAI may include a default configured NSSAI that the UE has in advance.

According to the second implementation of the present disclosure, for efficient PLMN selection, the UE may use the configured NSSAI stored in the non-volatile memory. When the UE receives an access failure per network slice for all S-NSSAI that can be transmitted for the current access network, the UE may check whether the S-NSSAI of another PLMN that can be accessed in the configured NSSAI stored in the non-volatile memory is the S-NSSAI related to the access failure per network slice. At this time, the UE may also check whether the default configured NSSAI exists.

According to the second implementation of the present disclosure, when selecting a PLMN from the VPLMN, a PLMN having a higher priority is selected from among HPLMN, EHPLMN, operator-controlled PLMN, and user-controlled PLMN. Therefore, without checking the S-NSSAI of all PLMNs in the configured NSSAI stored in the non-volatile memory of the UE, from among operator-controlled PLMN or user-controlled PLMN having a higher priority, the UE may check the S-NSSAI of all PLMNs existing in the configured NSSAI stored in the non-volatile memory.

According to the second implementation of the present disclosure, among the high-priority PLMNs, the UE may check whether the S-NSSAI of the PLMN that can be accessed in the configured NSSAI is the S-NSSAI related to the access failure per network slice, and if an S-NSSAI that is not related to the access failure per network slice exists for the corresponding PLMN, the UE may regard the corresponding PLMN as a candidate PLMN from which PLMN selection is possible. In addition, if all S-NSSAIs of the S-NSSAI that can be accessed to a certain network are S-NSSAIs related to the access failure per network slice, the UE may regard the corresponding PLMN as a PLMN that cannot be accessed. The UE may select only PLMNs considered to be accessible PLMNs based on S-NSSAI as the target of PLMN selection.

According to the second implementation of the present disclosure, in order to check whether it is an accessible PLMN, the UE may check whether all S-NSSAIs for each PLMN in the configured NSSAI stored in the non-volatile memory are S-NSSAIs related to the access failure per network slice as the NSSAI rejected in the previous network. If all S-NSSAIs of a specific PLMN are S-NSSAIs included in the rejected NSSAI that informed the access failure in the previous access network, the UE may regard the corresponding specific PLMN as a PLMN that cannot be accessed. If there is another S-NSSAI among the S-NSSAIs of the specific PLMN that is not included in the rejected NSSAI that informed the access failure in the previous access network, the UE may regard the corresponding specific PLMN as an accessible PLMN.

According to the second implementation of the present disclosure, when the default configured NSSAI exists, the UE may regard the corresponding specific PLMN as an accessible PLMN.

According to the second implementation of the present disclosure, in addition to or instead of the configured NSSAI stored in the non-volatile memory, the UE may determine whether a specific PLMN is an accessible PLMN based on the SLA that is an agreement between the VPLMN and the HPLMN.

The second implementation of the present disclosure is summarized as follows.

When performing a PLMN selection in a VPLMN, The UE does not consider the PLMN as valid in the following cases:

-   -   the UE is received with SGMM cause value #62 (No network slice         available);     -   the UE has configured NSSAI for that PLMN(s); and     -   all the S-NSSAI(s) in the configured NSSAI are in rejected NSSAI         with reject cause “S-NSSAI not available due to the failed or         revoked network slice-specific authentication and         authorization”.

According to the second implementation of the present disclosure, when the UE fails in the current access network due to failure of network slice specific authentication in the roaming state and selects a PLMN again, it does not select an unnecessary PLMN to fail again, so that the PLMN selection can be performed more efficiently.

3. Third Implementation

According to the third implementation of the present disclosure, for efficient PLMN selection in case of NSSAA failure, when a network entity (e.g., AMF) communicating with the UE informs the UE of the access failure of all network slices with the rejected NSSAI, the network entity may directly inform the UE of the PLMN that can be accessed through the corresponding network slice. That is, if the access to all S-NSSAI requested by the UE fails, the network entity may determine that the access will fail in the PLMN that the UE has selected using the corresponding S-NSSAI. And, if the network entity determines that the UE should perform PLMN selection again, the network entity may directly inform the UE of the PLMN that can be accessed through the corresponding network slice. Thereafter, the UE may perform PLMN selection using the PLMN selected and notified by the network entity.

According to the third implementation of the present disclosure, the network entity #1 that is directly related to (e.g., communicates with) the UE may request the network entity #2 of the PLMN to which the UE is accessible. Network entity #2 may determine a PLMN accessible to the UE and inform the network entity #1 thereof. The network entity #1 may inform the UE of the PLMN accessible to the UE received from the network entity #2. Alternatively, the network entity #2 may directly inform the UE of the PLMN accessible to the UE, and the UE may perform PLMN selection using the PLMN selected and notified by the network entity #2. Alternatively, the PLMN selection may be performed directly with the corresponding PLMN notified by the network. Network entity #1 may be an AMF. Network entity #2 may be UDM or SOR application function (AF).

According to the third implementation of the present disclosure, when the network entity #2 that directly informs the UE of an accessible PLMN is SOR AF, PLMN information may be configured as follows.

The network may transmit the PLMN information to the UE using a DL NAS transport message. At this time, the payload container type in the DL NAS transport message may be configured to a SOR transparent container. The PLMN list indicating the accessible PLMN may be transmitted encrypted by the SIM, or may inform the PLMN ID and the access technology list in an unencrypted state. Upon receiving this, the UE may store it in mobile equipment (ME) and use the value stored in the ME, or may use the value stored in the SIM.

Table 3 shows an example of a DL NAS transport message according to the third implementation of the present disclosure.

TABLE 3 IEI Information Element Type/Reference Presence Format Length Extended protocol Extended protocol M V 1 discriminator discriminator 9.2 Security header Security header M V ½ type type 9.3 Spare half octet Spare half octet M V ½ 9.5 DL NAS Message type M V 1 TRANSPORT 9.7 message identity Payload container Payload container M V ½ type type 9.11.3.40 Spare half octet Spare half octet M V ½ 9.5 Payload container Payload container M LV-E 3-65537 9.11.3.39 12 PDU session ID PDU session C TV 2 identity 29.11.3.41 24 Additional Additional O TLV 3-n information information 9.11.2.1 58 5GMM cause 5GMM cause O TV 2 9.11.3.2 37 Back-off timer value GPRS timer O TLV 3 39.11.2.5

FIGS. 10 and 11 show an example of an SOR transparent container IE according to the third implementation of the present disclosure.

FIG. 10 shows an SOR transparent container IE when the value of the list type is 0 and the value of the SOR data type is 0. FIG. Referring to FIG. 10, the SOR transparent container IE may include a secured packet, and the secured packet may include a PLMN list.

FIG. 11 shows an SOR transparent container IE when the value of the list type is 1 and the value of the SOR data type is 0. Referring to FIG. 11, the SOR transparent container IE includes a PLMN ID and the access technology list.

When the UE receives an available PLMN ID from the network, the UE may regard it as a preferred PLMN, and may preferentially find the corresponding PLMN when selecting a PLMN. Since the corresponding PLMN is received from the network, the corresponding PLMN may be set as a PLMN having the highest priority in a value of “Operator Controlled PLMN selector with Access Technology” in the USIM. Alternatively, the corresponding PLMN may be set as the highest priority PLMN in the preferred PLMN stored in the ME. Thereafter, the UE may perform PLMN selection in consideration of a preferred PLMN when selecting a PLMN.

According to the third implementation of the present disclosure, when the network entity #1 (e.g., AMF) informs the UE of an accessible PLMN, the PLMN information may be included in the registration reject message and/or deregistration request message and transmitted. In this case, one piece of PLMN information may be included or a list of possible PLMNs may be included.

Table 4 shows an example of a deregistration request message according to the third implementation of the present disclosure.

TABLE 4 IEI Information Element Type/Reference Presence Format Length Extended protocol Extended protocol M V 1 discriminator discriminator 9.2 Security header type Security header M V ½ type 9.3 Spare half octet Spare half octet M V ½ 9.5 De-registration Message type M V 1 request 9.7 message identity De-registration type De-registration M V ½ type 9.11.3.20 Spare half octet Spare half octet M V ½ 9.5 58 5GMM cause 5GMM cause O TV 2 9.11.3.2 5F T3346 value GPRS timer O TLV 3 29.11.2.4 6D Rejected NSSAI Rejected NSSAI O TLV 4-42 9.11.3.46 Selected PLMN PLMN list O TLV 5-47 9.11.3.45

Referring to Table 4, the deregistration request message includes a “Selected PLMN” IE.

When the UE receives PLMN information through a deregistration request message and/or a registration reject message from the network, the UE regards the corresponding PLMN as a preferred PLMN having a high priority, and may preferentially find the corresponding PLMN when selecting the PLMN.

4. Fourth Implementation

According to the fourth implementation of the present disclosure, in order to determine a PLMN having a failed S-NSSAI, the UE may first select a PLMN having a higher priority among priority PLMNs stored in the SIM (e.g., user controlled PLMN selector with access technology or operator controlled PLMN selector with access technology) and may determine a list of accessible PLMNs. From the list of accessible PLMNs found by the network, if all S-NSSAIs of the corresponding PLMN are related to the rejected NSSAI due to NSSAA failure, the UE may determine the corresponding PLMN as a PLMN not considered in PLMN selection. Thereafter, the network may perform PLMN selection by using the remaining PLMNs, etc., excluding PLMNs that are not considered in PLMN selection.

According to the fourth implementation of the present disclosure, when receiving the selected PLMN information from the network, the UE may set the received PLMN to the value of the operator controlled PLMN selector with access technology stored in the SIM or ME as the value having the highest priority.

Claims in the present disclosure can be combined in a various way. For instance, technical features in method claims of the present disclosure can be combined to be implemented or performed in an apparatus, and technical features in apparatus claims can be combined to be implemented or performed in a method. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in an apparatus. Further, technical features in method claim(s) and apparatus claim(s) can be combined to be implemented or performed in a method. Other implementations are within the scope of the following claims. 

What is claimed is:
 1. A method performed by a user equipment (UE) operating in a wireless communication system, the method comprising: obtaining default configured network slice selection assistance information (NSSAI) which can be used in a first public land mobile network (PLMN); generating first requested NSSAI including a first single NSSAI (S-NSSAI) corresponding to a network slice to which the UE requests to register with; transmitting, to an access and mobility management function (AMF) of the first PLMN, a first registration request message including the first requested NSSAI; receiving, from the AMF of the first PLMN, a registration reject message in response to the first registration request message, wherein the registration reject message includes rejected NSSAI including the first S-NSSAI, wherein the registration reject message includes a cause value #62 for the rejected NSSAI, and wherein the cause value #62 indicates “No network slices available”; based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with: generating second requested NSSAI including the second S-NSSAI; and transmitting, to the AMF of the first PLMN, a second registration request message including the second requested NSSAI.
 2. The method of claim 1, wherein the default NSSAI is valid in a PLMN where the UE does not have the allowed NSSAI and the configured NSSAI.
 3. The method of claim 1, wherein the default NSSAI is obtained from a home PLMN (HPLMN).
 4. The method of claim 1, wherein the UE does not have the allowed NSSAI and the configured NSSAI for the first PLMN.
 5. The method of claim 4, wherein the UE not having the allowed NSSAI and the configured NSSAI for the first PLMN comprises removing the first S-NSSAI included in the rejected NSSAI from the allowed NSSAI for the first PLMN and/or the configured NSSAI for the first PLMN.
 6. The method of claim 1, wherein the allowed NSSAI is obtained from the AMF of the first PLMN through a registration accept message for the first PLMN.
 7. The method of claim 1, wherein the configured NSSAI is configured by the first PLMN.
 8. The method of claim 1, wherein the second registration request message is transmitted without PLMN selection.
 9. The method of claim 1, wherein the UE communicates with at least one of a mobile device, a network and/or an autonomous vehicle other than the UE.
 10. A user equipment (UE) operating in a wireless communication system, the wireless device comprising: at least one transceiver; at least one processor; and at least one memory operably connectable to the at least one processor and storing instructions that, based on being executed by the at least one processor, perform operations comprising: obtaining default configured network slice selection assistance information (NSSAI) which can be used in a first public land mobile network (PLMN); generating first requested NSSAI including a first single NSSAI (S-NSSAI) corresponding to a network slice to which the UE requests to register with; transmitting, to an access and mobility management function (AMF) of the first PLMN, a first registration request message including the first requested NSSAI; receiving, from the AMF of the first PLMN, a registration reject message in response to the first registration request message, wherein the registration reject message includes rejected NSSAI including the first S-NSSAI, wherein the registration reject message includes a cause value #62 for the rejected NSSAI, and wherein the cause value #62 indicates “No network slices available”; based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with: generating second requested NSSAI including the second S-NSSAI; and transmitting, to the AMF of the first PLMN, a second registration request message including the second requested NSSAI.
 11. The UE of claim 10, wherein the default NSSAI is valid in a PLMN where the UE does not have the allowed NSSAI and the configured NSSAI.
 12. The UE of claim 10, wherein the UE does not have the allowed NSSAI and the configured NSSAI for the first PLMN.
 13. The UE of claim 12, wherein the UE not having the allowed NSSAI and the configured NSSAI for the first PLMN comprises removing the first S-NSSAI included in the rejected NSSAI from the allowed NSSAI for the first PLMN and/or the configured NSSAI for the first PLMN.
 14. The UE of claim 10, wherein the second registration request message is transmitted without PLMN selection.
 15. An apparatus operating in a wireless communication system, the apparatus comprising: at least one processor; and at least one memory operably connectable to the at least one processor, wherein the at least one processor is configured to perform operations comprising: obtaining default configured network slice selection assistance information (NSSAI) which can be used in a first public land mobile network (PLMN); generating first requested NSSAI including a first single NSSAI (S-NSSAI) corresponding to a network slice to which the UE requests to register with; generating a first registration request message including the first requested NSSAI; obtaining a registration reject message in response to the first registration request message, wherein the registration reject message includes rejected NSSAI including the first S-NSSAI, wherein the registration reject message includes a cause value #62 for the rejected NSSAI, and wherein the cause value #62 indicates “No network slices available”; based on i) the UE not having allowed NSSAI and configured NSSAI, and ii) the default configured NSSAI including a second S-NSSAI not included in the rejected NSSAI and corresponding to a network slice to which the UE requests to register with: generating second requested NSSAI including the second S-NSSAI; and generating a second registration request message including the second requested NSSAI. 